Abstract– In this interview, Joseph Goldstein ( Fig. 1 ) recounts how he became interested in meteorites during his graduate studies working with Robert Ogilvie at MIT. By matching the Ni profiles observed across taenite fields in the Widmanstätten structure of iron meteorites with profiles he computed numerically he was able to determine cooling rates as the meteorites cooled through 650–400 °C. Upon graduating, he worked with a team of meteorite researchers led by Lou Walter at Goddard Space Flight Center where for 4 years he attempted to understand metallographic structures by reproducing them in the laboratory. Preferring an academic environment, Joe accepted a faculty position in the rapidly expanding metallurgy department at Lehigh University where he was responsible for their new electron microprobe. He soon became involved in studying the metal from lunar soils and identifying the metallic component from its characteristic iron and nickel compositions. Over the next two decades he refined these studies of Ni diffusion in iron meteorites, particularly the effect of phosphorus in the process, which resulted in superior Fe‐Ni‐P phase diagrams and improved cooling rates for the iron meteorites. After a period as vice president for research at Lehigh, in 1993 he moved to the University of Massachusetts to serve as dean of engineering, but during these administrative appointments Joe produced a steady stream of scientific results. Joe has served as Councilor, Treasurer, Vice President, and President of the Meteoritical Society. He received the Leonard Medal in 2005, the Sorby Award in 1999, and the Dumcumb Award for in 2008. Figure 1 Open in figure viewer PowerPoint Joseph Goldstein. 相似文献
A parent body of the Lovina meteorite underwent processes which yielded dentritic structures of taenite in phosphide-sulfide-metal
matrix unusual for iron meteorites. Similar dendritic structures can be found also in IIE meteorites as microinclusions but
are unknown in other iron meteorites. The similarity between dendritic structures in the Lovina meteorite and metal-phosphide
inclusions in IIE iron meteorites implies similar processes which led to their crystallization from molten materials in chambers
of various sizes. Studying physical and chemical crystallization parameters of metal-phosphide inclusions in the Elga meteorite
(IIE) makes it feasible to estimate the p-T conditions required for the unique Lovina meteorite to have formed. It is shown
that dendrites in the Lovina meteorite may have been crystallized from molten materials close in composition to P-FeNi and
P-S-FeNi that are produced when phosphides and sulfides melt locally in metals as a result of impact events with subsequent
fast cooling. The temperature of homogeneous melting is likely to have been more than 1450°C, and the starting temperature
of crystallization of such molten materials is estimated to have been between 1050 and 1150°C. The cooling rate of inclusions
can be estimated to be 10−3 °C s−1, based on the structural and chemical concordance between samples obtained experimentally (Chabot et al., 2000) and metal-phosphide
inclusions (P-FeNi and P-S-FeNi) in the Elga meteorite. Large-sized dendrites in the Lovina meteorite imply cooling rates
that are considerably less than 10−3 °C s−1. 相似文献
Cadmium is a highly volatile element and its abundance in meteorites may help better understand volatility‐controlled processes in the solar nebula and on meteorite parent bodies. The large thermal neutron capture cross section of 113Cd suggests that Cd isotopes might be well suited to quantify neutron fluences in extraterrestrial materials. The aims of this study were (1) to evaluate the range and magnitude of Cd concentrations in magmatic iron meteorites, and (2) to assess the potential of Cd isotopes as a neutron dosimeter for iron meteorites. Our new Cd concentration data determined by isotope dilution demonstrate that Cd concentrations in iron meteorites are significantly lower than in some previous studies. In contrast to large systematic variations in the concentration of moderately volatile elements like Ga and Ge, there is neither systematic variation in Cd concentration amongst troilites, nor amongst metal phases of different iron meteorite groups. Instead, Cd is strongly depleted in all iron meteorite groups, implying that the parent bodies accreted well above the condensation temperature of Cd (i.e., ≈650 K) and thus incorporated only minimal amounts of highly volatile elements. No Cd isotope anomalies were found, whereas Pt and W isotope anomalies for the same iron meteorite samples indicate a significant fluence of epithermal and higher energetic neutrons. This observation demonstrates that owing to the high Fe concentrations in iron meteorites, neutron capture mainly occurs at epithermal and higher energies. The combined Cd‐Pt‐W isotope results from this study thus demonstrate that the relative magnitude of neutron capture‐induced isotope anomalies is strongly affected by the chemical composition of the irradiated material. The resulting low fluence of thermal neutrons in iron meteorites and their very low Cd concentrations make Cd isotopes unsuitable as a neutron dosimeter for iron meteorites. 相似文献
Iron meteorites provide a record of the thermal evolution of their parent bodies, with cooling rates inferred from the structures observed in the Widmanstätten pattern. Traditional planetesimal thermal models suggest that meteorite samples derived from the same iron core would have identical cooling rates, possibly providing constraints on the sizes and structures of their parent bodies. However, some meteorite groups exhibit a range of cooling rates or point to uncomfortably small parent bodies whose survival is difficult to reconcile with dynamical models. Together, these suggest that some meteorites are indicating a more complicated origin. To date, thermal models have largely ignored the effects that impacts would have on the thermal evolution of the iron meteorite parent bodies. Here we report numerical simulations investigating the effects that impacts at different times have on cooling rates of cores of differentiated planetesimals. We find that impacts that occur when the core is near or above its solidus, but the mantle has largely crystallized can expose iron near the surface of the body, leading to rapid and nonuniform cooling. The time period when a planetesimal can be affected in this way can range between 20 and 70 Myr after formation for a typical 100 km radius planetesimal. Collisions during this time would have been common, and thus played an important role in shaping the properties of iron meteorites. 相似文献
The acapulcoite‐lodranite meteorites are members of the primitive achondrite class. The observation of partial melting and resulting partial removal of Fe‐FeS indicates that this meteorite group could be an important link between achondrite and iron meteorites, on the one hand, and chondrite meteorites, on the other. Thus, a better understanding of the thermomechanical evolution of the parent body of this meteorite group can help improve our understanding of the evolution of early planetesimals. Here, we use 2‐D and 3‐D finite‐difference numerical models to determine the formation time, initial radius of the parent body of the acapulcoite‐lodranite meteorites, and their formation depth inside the body by applying available geochronological, thermal, and textural constraints to our numerical data. Our results indicate that the best fit to the data can be obtained for a parent body with 25–65 km radius, which formed around 1.3 Ma after calcium‐aluminum‐rich inclusions. The 2‐D and 3‐D results considering various initial temperatures and the effect of porosity indicate possible formation depths of the acapulcoite‐lodranite meteorites of 9–19 and 14–25 km, respectively. Our data also suggest that other meteorite classes could form at different depths inside the same parent body, supporting recently proposed models (Elkins‐Tanton et al. 2011 ; Weiss and Elkins‐Tanton 2013 ). 相似文献
Noble gases and nitrogen were measured in two adjacent samples each from the Raghunathpura (IIAB) and the Nyaung (IIIAB) iron meteorite falls. Light noble gases in both the meteorites were of pure cosmogenic origin. Using (3He/4He)c ratios and the production systematic of Ammon et al. ( 2009 ), we estimated the sample depth and meteoroid size for Nyaung (~8 cm depth in a ~15 cm radius object) and Raghunathpura (~12–14 cm depth in a ~25 cm object). We derived cosmic ray exposure ages of 1710 ± 256 Ma (for Nyaung, the highest reported so far for the IIIAB group) and 224 ± 34 Ma (for Raghunathpura). Variable amounts of trapped Kr and Xe were found in both meteorites. The phase Q‐like elemental ratio (84Kr/132Xe) suggests that the trapped component is of indigenous origin, and most likely hosted in the heterogeneously distributed micro‐inclusions of troilite/schreibersite. Trapped phase Q component is being reported for the first time, for a IIAB iron meteorite. Both meteorites showed light isotopic composition for nitrogen, and need at least two N components to explain the observed N isotopic systematic. Variable amounts of trapped noble gases and the presence of more than one N component suggest that the magmatic process that formed the parent body of these meteorites either could not completely homogenize or completely degas all the phases. 相似文献
Abstract— Stuart H. Perry (1874–1957), an influential Michigan newspaper editor and publisher and a vice president of the Associated Press, developed a passionate interest in collecting and studying meteorites in the 1920s and 1930s. Firmly believing that meteorites belong in great museums where they can be properly investigated, he generously donated his meteorites to various museums after he finished his own study of them. He had a sincere interest in the National Collection of Meteorites, and donated 192 specimens–‐mostly irons–‐to the U.S. National Museum; these constituted some of the most important meteorites in its collection, and moved iron meteorites to center stage, a position still occupied. By applying current metallographic methods to the study of iron meteorites, Perry directed scientists to a powerful new research tool, which led to major advances in our understanding of meteoritic irons and helped give rise to a new field within planetary sciences. His groundbreaking monograph The metallography of meteoric iron served as a standard reference collection of metallographic photomicrographs of iron meteorites for more than 30 years. It remained an insightful and useful work on the structure of meteoritic iron until improved binary and ternary phase diagrams in the Fe‐Ni(‐P) system allowed a more detailed treatment of the formation of iron meteorites. Perry received many honors for his work, and held office in the Meteoritical Society, serving as a councilor from 1941–1950, and as a vice president from 1950–1957. 相似文献
The bulk chlorine concentrations and isotopic compositions of a suite of non‐carbonaceous (NC) and carbonaceous (CC) iron meteorites were measured using gas source mass spectrometry. The δ37Cl values of magmatic irons range from ?7.2 to 18.0‰ versus standard mean ocean chloride and are unrelated to their chlorine concentrations, which range from 0.3 to 161 ppm. Nonmagmatic IAB irons are comparatively Cl‐rich containing >161 ppm with δ37Cl values ranging from ?6.1 to ?3.2‰. The anomalously high and low δ37Cl values are inconsistent with a terrestrial source, and as Cl contents in magmatic irons are largely consistent with derivation from a chondrite‐like silicate complement, we suggest that Cl is indigenous to iron meteorites. Two NC irons, Cape York and Gibeon, have high cooling rates with anomalously high δ37Cl values of 13.4 and 18.0‰. We interpret these high isotopic compositions to result from Cl degassing during the disruption of their parent bodies, consistent with their low volatile contents (Ga, Ge, Ag). As no relevant mechanisms in iron meteorite parent bodies are expected to decrease δ37Cl values, whereas volatilization is known to increase δ37Cl values by the preferential loss of light isotopes, we interpret the low isotope values of <?5‰ and down to ?7.2‰ to most closely represent the primordial isotopic composition of Cl in the solar nebula. Similar conclusions have been derived from low δ37Cl values down to ?6, and ?3.8‰ measured in Martian and Vestan meteorites, respectively. These low δ37Cl values are in contrast to those of chondrites which average around 0‰ previously explained by the incorporation of isotopically heavy HCl clathrate into chondrite parent bodies. The poor retention of low δ37Cl values in many differentiated planetary materials suggest that extensive devolatilization occurred during planet formation, which can explain Earth's high δ37Cl value by the loss of approximately 60% of the initial Cl content. 相似文献
We present high precision, low‐ and high‐resolution tungsten isotope measurements of iron meteorites Cape York (IIIAB), Rhine Villa (IIIE), Bendego (IC), and the IVB iron meteorites Tlacotepec, Skookum, and Weaver Mountains, as well as CI chondrite Ivuna, a CV3 chondrite refractory inclusion (CAI BE), and terrestrial standards. Our high precision tungsten isotope data show that the distribution of the rare p‐process nuclide 180W is homogeneous among chondrites, iron meteorites, and the refractory inclusion. One exception to this pattern is the IVB iron meteorite group, which displays variable excesses relative to the terrestrial standard, possibly related to decay of rare 184Os. Such anomalies are not the result of analytical artifacts and cannot be caused by sampling of a protoplanetary disk characterized by p‐process isotope heterogeneity. In contrast, we find that 183W is variable due to a nucleosynthetic s‐process deficit/r‐process excess among chondrites and iron meteorites. This variability supports the widespread nucleosynthetic s/r‐process heterogeneity in the protoplanetary disk inferred from other isotope systems and we show that W and Ni isotope variability is correlated. Correlated isotope heterogeneity for elements of distinct nucleosynthetic origin (183W and 58Ni) is best explained by thermal processing in the protoplanetary disk during which thermally labile carrier phases are unmixed by vaporization thereby imparting isotope anomalies on the residual processed reservoir. 相似文献
Abstract– Klaus Keil ( Fig. 1 ) grew up in Jena and became interested in meteorites as a student of Fritz Heide. His research for his Dr. rer. nat. became known to Hans Suess who––with some difficulty––arranged for him to move to La Jolla, via Mainz, 6 months before the borders of East Germany were closed. In La Jolla, Klaus became familiar with the electron microprobe, which has remained a central tool in his research and, with Kurt Fredriksson, he confirmed the existence of Urey and Craig’s chemical H and L chondrite groups, and added a third group, the LL chondrites. Klaus then moved to NASA Ames where he established a microprobe laboratory, published his definitive paper on enstatite chondrites, and led in the development of the Si(Li) detector and the EDS method of analysis. After 5 years at Ames, Klaus became director of the Institute of Meteoritics at the University of New Mexico where he built up one of the leading meteorite research groups while working on a wide variety of projects, including chondrite groups, chondrules, differentiated meteorites, lunar samples, and Hawai’ian basalts. The basalt studies led to a love of Hawai’i and a move to the University of Hawai’i in 1990, where he has continued a wide variety of meteorite projects, notably the role of volcanism on asteroids. Klaus Keil has received honorary doctorates from Friedrich‐Schiller University, Jena, and the University of New Mexico, Albuquerque. He was President of the Meteoritical Society in 1969–1970 and was awarded the Leonard Medal in 1988. Figure 1 Open in figure viewer PowerPoint Klaus Keil at the University of Hawai’i at Manoa, 2007. 相似文献
Measurements of Ni concentration profiles of a large number of neighboring kamacite and taenite lamellae in the iron meteorite Cape York (IIIA) have revealed that the kamacite plates have nucleated in a taenite of varying Ni concentration, equal to or above the bulk Ni concentration of the meteorite. This variation indicates that the kamacite plates nucleated stepwise (i.e., independently) during cooling through a certain temperature interval, rather than simultaneously after more or less undercooling of the meteorite. The latter is assumed in most previous cooling rate determinations (e.g., Moren and Goldstein, 1978). In this paper the measured local bulk Ni concentrations are used in the computer simulation of the evolution of the Widmannstaetten pattern in order to calculate the cooling rate of the meteorite. The cooling rate obtained for Cape York is 1.3°K/my. In most previous work, a correlation is seen between the resulting taenite width and the cooling rate in one and the same meteorite. No such correlation is seen using the present method. 相似文献
We report the first combined atom‐probe tomography (APT) and transmission electron microscopy (TEM) study of a kamacite–tetrataenite (K–T) interface region within an iron meteorite, Bristol (IVA). Ten APT nanotips were prepared from the K–T interface with focused ion beam scanning electron microscopy (FIB‐SEM) and then studied using TEM followed by APT. Near the K‐T interface, we found 3.8 ± 0.5 wt% Ni in kamacite and 53.4 ± 0.5 wt% Ni in tetrataenite. High‐Ni precipitate regions of the cloudy zone (CZ) have 50.4 ± 0.8 wt% Ni. A region near the CZ and martensite interface has <10 nm sized Ni‐rich precipitates with 38.4 ± 0.7 wt% Ni present within a low‐Ni matrix having 25.5 ± 0.6 wt% Ni. We found that Cu is predominantly concentrated in tetrataenite, whereas Co, P, and Cr are concentrated in kamacite. Phosphorus is preferentially concentrated along the K‐T interface. This study is the first precise measurement of the phase composition at high spatial resolution and in 3‐D of the K‐T interface region in a IVA iron meteorite and furthers our knowledge of the phase composition changes in a fast‐cooled iron meteorite below 400 °C. We demonstrate that APT in conjunction with TEM is a useful approach to study the major, minor, and trace elemental composition of nanoscale features within fast‐cooled iron meteorites. 相似文献
Abstract— Batch culture experiments were performed to investigate the weathering of meteoritic material by iron‐oxidizing bacteria. The aerobic, acidophilic iron oxidizer (A. ferrooxidans) was capable of oxidizing iron from both carbonaceous chondrites (Murchison and Cold Bokkeveld) and iron meteorites (York and Casas Grandes). Preliminary iron isotope results clearly show contrasted iron pathways during oxidation with and without bacteria suggesting that a biological role in meteorite weathering could be distinguished isotopically. Anaerobic iron‐oxidizers growing under pH‐neutral conditions oxidized iron from iron meteorites. These results show that rapid biologically‐mediated alteration of extraterrestrial materials can occur in both aerobic and anaerobic environments. These results also demonstrate that iron can act as a source of energy for microorganisms from both iron and carbonaceous chondrites in aerobic and anaerobic conditions with implications for life on the early Earth and the possible use of microorganisms to extract minerals from asteroidal material. 相似文献
Abstract— We describe an analytical technique for measurements of Fe, Ni, Co, Mo, Ru, Rh, W, Re, Os, Ir, Pt, and Au in bulk samples of iron meteorites. The technique involves EPMA (Fe, Ni, Co) and LA‐ICP‐MS analyses of individual phases of iron meteorites, followed by calculation of bulk compositions based on the abundances of these phases. We report, for the first time, a consistent set of concentrations of Mo, Ru, Rh, Pd, W, Re, Os, Ir, Pt, and Au in the iron meteorites Arispe, Bennett County, Grant, Cape of Good Hope, Cape York, Carbo, Chinga, Coahuila, Duchesne, Gibeon, Henbury, Mundrabilla, Negrillos, Odessa, Sikhote‐Alin, and Toluca and the Divnoe primitive achondrite. The comparison of our LA‐ICP‐MS data for a number of iron meteorites with high‐precision isotope dilution and INAA data demonstrates the good precision and accuracy of our technique. The narrow ranges of variations of Mo and Pd concentrations within individual groups of iron meteorites suggest that these elements can provide important insights into the evolution of parent bodies of iron meteorites. Under certain assumptions, the Mo concentrations can be used to estimate mass fractions of the metal‐sulfide cores in the parent bodies of iron meteorites. It appears that a range of Pd variations within a group of iron meteorites can serve as a useful indicator of S content in the core of its parent body. 相似文献
Fossil iron meteorites are extremely rare in the geological sedimentary record. The paleometeorite described here is the first such finding at the Cretaceous‐Paleogene (K‐Pg) boundary. In the boundary clay from the outcrop at the Lechówka quarry (Poland), fragments of the paleometeorite were found in the bottom part of the host layer. The fragments of meteorite (2–6 mm in size) and meteoritic dust are metallic‐gray in color and have a total weight of 1.8181 g. Geochemical and petrographic analyses of the meteorite from Lechówka reveal the presence of Ni‐rich minerals with a total Ni amount of 2–3 wt%. The identified minerals are taenite, kamacite, schreibersite, Ni‐rich magnetite, and Ni‐rich goethite. No relicts of silicates or chromites were found. The investigated paleometeorite apparently represents an independent fall and does not seem to be derived from the K‐Pg impactor. The high degree of weathering did not permit the chemical classification of the meteorite fragments. However, the recognized mineral inventory, lack of silicates, and their pseudomorphs and texture may indicate that the meteorite remains were an iron meteorite. 相似文献
The Whitecourt meteorite impact crater, Alberta, Canada is a rare example of a well‐preserved small impact structure, with which thousands of meteorite fragments are associated. As such, this crater represents a unique opportunity to investigate the effect of a low‐energy impact event on an impacting iron bolide. Excellent documentation of meteorite fragment locations and characteristics has generated a detailed distribution map of both shrapnel and regmaglypted meteorite types. The meteorites' distribution, and internal and external characteristics support a low‐altitude breakup of the impactor which caused atmospherically ablated (regmaglypted) meteorites to fall close to the crater and avoid impact‐related deformation. In contrast, shrapnel fragments sustained deformation at macro‐ and microscales resulting from the catastrophic disruption of the impactor. The impactor was significantly fragmented along pre‐existing planes of weakness, including kamacite lamellae and inclusions, resulting in a bias toward low‐mass (<100 g) fragments. Meteorite mineralogy was investigated and the accessory minerals were found to be dominated by sulfides and phosphides with rare carlsbergite, consistent with other low‐Ni IIIAB iron meteorites. Considerations of the total mass of meteoritic material recovered at the site relative to the probable fraction of the impactor that was preserved based on modeling suggests that the crater was formed by a higher velocity, lower mass impactor than previously inferred. 相似文献
Abstract— Nine additional iron meteorite fragments weighing a total of 72 kg were recovered from the Derrick Peak area by a Canterbury Museum geological party in late 1988. One iron was located in the Onnum Valley, 6 km south of the previous finds. Geochemical analysis indicates that all irons belong to a single meteorite shower, greatly increasing the known extent of the fall zone. Kamp and Lowe (1982) have previously estimated the terrestrial age of the meteorite from glacial geological evidence. The location of the 1988 finds supports Kamp and Lowe's interpretation that the meteorites lie in situ, but recent revisions of the chronology of Cenozoic glacial history of the region reduce the interpreted terrestrial age. An age of between Oxygen Isotope stages 6 and 2 is probable (190–125 to 35–12 ka BP). This conflicts with a terrestrial age estimate of 1.0 ± 0.1 Ma BP from cosmogenic radionuclides. 相似文献
Mössbauer spectra of equilibrated ordinary chondrites consist of two doublets due to paramagnetic iron present in olivines and pyroxenes and two sextets due to magnetically ordered iron present in metallic phases and troilite. The spectral areas of the different mineralogical phases found by Mössbauer spectroscopy in meteorites are proportional to the number of iron atoms in this mineralogical phase. This property of Mössbauer spectra can be the basis for constructing a method for the classification of ordinary chondrites. This idea was first explored at the Mössbauer Laboratory in Kanpur. This group suggested a qualitative method based on 2‐dimensional plots of Mössbauer spectral areas and thus classified properly some meteorites. We constructed a quantitative method using Mössbauer spectral areas, multidimensional discriminant analysis, and Mahalanobis distance (4M method) to determine the probability of a meteorite to be of type H, L, or LL. Based on 59 Mössbauer spectra, we calculated by the 4M method, S cluster , the level of similarity of the Goronyo meteorite to the clusters. On the plot of ferrosilite versus fayalite, the point representing Goronyo is located on the border between H and L areas. Calculated by the 4M method, the meteorite Goronyo is 32% similar to type H, 75% to type L, and 11% to type LL. Additional mineralogical analyses suggested that the Goronyo meteorite would be classified as type L, although it was originally reported as type H in the Meteoritical Bulletin Database. 相似文献
We have studied the Mukundpura CM2 meteorite for magnetic properties as a function of temperature and magnetic field, as well as its Mössbauer spectrum, at room and low temperatures (up to 5 K). We find that the high temperature paramagnetic phase is followed by two magnetic transitions: a weak transition near 125 K and a strong transition at 8 K. The weak (125 K) magnetic phase can be attributed to complex Fe2+–Fe3+ constituents present in the meteorite. The absence of the characteristic sextet corresponding to magnetite in Mossbauer spectrum indicates that this magnetic phase is not magnetite, which, if present, must be in insignificant amount. The 8 K magnetic ordering is superimposed with weak ferromagnetic ordering, showing spin‐glass transition. The Mössbauer spectrum taken at 5 K substantiates the observed spin‐glassy nature, as very large hyperfine field ~32 T is recorded, causing localized subordering leading to spin‐glass behavior. The Mössbauer spectra also confirm that iron is mainly present in serpentine‐group minerals, both in ferrous and ferric states. The complete serpentinization of basic silicates indicates aggressive hydrous alteration. These results show that the observed spin‐glass signature is a characteristic feature of the cronstedtite phase in CM meteorites. This feature is unique to carbonaceous CM chondrites and could be used for nondestructive, quick, and independent classification of this rare class of meteorites. Furthermore, the absence of olivine and the presence of cronstedtite in Mossbauer spectra show that the degree of aqueous alteration observed is the most severe in Mukundpura CM2 meteorite, as compared to many other CM2 meteorites. The degree of aqueous alteration in CM2 carbonaceous chondrites increases in the sequence: Paris, Murchison, Murray, Mighei, Nogoya, Cold Bokkeveld, and Mukundpura. 相似文献
We measured specific activities of the long‐lived cosmogenic radionuclides 60Fe in 28 iron meteorites and 53Mn in 41 iron meteorites. Accelerator mass spectrometry was applied at the 14 MV Heavy Ion Accelerator Facility at ANU Canberra for all samples except for two which were measured at the Maier‐Leibnitz Laboratory, Munich. For the large iron meteorite Twannberg (IIG), we measured six samples for 53Mn. This work doubles the number of existing individual 60Fe data and quadruples the number of iron meteorites studied for 60Fe. We also significantly extended the entire 53Mn database for iron meteorites. The 53Mn data for the iron meteorite Twannberg vary by more than a factor of 30, indicating a significant shielding dependency. In addition, we performed new model calculations for the production of 60Fe and 53Mn in iron meteorites. While the new model is based on the same particle spectra as the earlier model, we no longer use experimental cross sections but instead use cross sections that were calculated using the latest version of the nuclear model code INCL. The new model predictions differ substantially from results obtained with the previous model. Predictions for the 60Fe activity concentrations are about a factor of 2 higher, for 53Mn, they are ~30% lower, compared to the earlier model, which gives now a better agreement with the experimental data. 相似文献
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